Modern automobiles have a high level of electronic equipment. As a result the reliability of electrical power supply of a vehicle is important. The inability to detect problems, and provide an early warning of problems, extracts from the reliability of the vehicle electrical power system.
Many types of secondary storage batteries are used in the vehicle industry such as, for example, lead acid battery, nickel-cadmium battery, silver cadmium battery, and others. The most popularly used in the vehicle industry is the lead-acid battery.
Chemical storage batteries, such as lead acid batteries used in automobiles, have existed for nearly a century with much improvement in reliability. However, due to the critical working environment of the battery such as, for example wide range of operating temperatures and high cranking currents, battery power failure is still unpredictable and may at times be without warning.
A vehicle electrical power system consists of a battery, an alternator, and loads. The loads include the starter motor. The battery is the key component of the vehicle electrical power system. The battery is mainly for starting, lighting and ignition. The battery receives energy from the alternator, and supplies energy to the starter motor and other loads. Any defective element in the power system will cause system failure.
Presently, various techniques are used to determine battery status. For example, one may use the measurement of the specific gravity of the electrolyte, the measurement of open circuit voltage; the measurement of internal resistance, conductance, capacity, and cranking current, by using AC or DC source or load. A more popular method uses a load tester (Hundreds-Ampere-Second discharge) to test the battery with a high current discharge for a few seconds. It monitors voltage changes to determine battery status.
However, these tests are not the actual load on the battery under operating conditions. They are only indicative of battery status. They only indicate the condition of the battery with an open circuit and without load or charging current. This means that such testing is under “off line” conditions that provide only static data. Hence, these methods do not provide an accurate, dynamic measurement when there is interference by charging current, load current, ripple noise, and other noises, which exist in an actual operating environment.
Cranking Ampere (“CA”) or Cool Cranking Ampere (“CCA”) and State of Charge (“SOC”) are important parameters of a battery. The cranking current capacity or cranking current percentage of a battery can only be determined by comparing the measured data with the manufacturer's reference data. A positive determination given by a CA or CCA test may not be correct if the battery is undersized for a particular application. The SOC indicates the charge percentage status of a battery. However, if the capacity of the battery is degraded, the SOC cannot used to determine the actual capacity of the battery.